1. Field of the Invention
The present invention relates to a key for coupling a driving member and a driven member together, and more particularly, to a key not only capable of being securely fitted into a key groove provided between the driving member and the driven member without damaging the members, but also capable of being easily drawn out from the key groove which receives the key.
2. Description of the Related Arts
Commonly used is a key to couple together a driving member and a driven member, for example, a rotational driving shaft and a rotational driven shaft which is rotated by the driving shaft. More specifically, between the drive and driven members there is provided a tapered key groove which receives a tapered key adapted to be fitted to the key groove. The head of the key is then struck with a hammer or a hydraulically driven tool to drive and fit the key into the key groove for coupling the driving member and the driven member together.
However, the use of such conventional key often damages the driving and driven members due to a shock which may be caused by striking the key with the hammer or the like to fit the key into the key groove. Particularly, in the case where the driving and driven members are optical instruments or precision instruments such as a drive system of a servomotor for use in a precise machine tool and the like, such damage leads directly to a defective products and hence is not allowable.
Moreover, it is difficult in the conventional key to again draw out the key from the key groove once fitting the key into the key groove as described above, and the instruments may be further damaged if the key is forcibly extracted from the key groove.
While on the contrary, in the case where the driving and driven members are the rotational driving shaft and the rotational driven shaft which is rotated following the driving shaft, respectively, there exists a gap, for example, of the order of 0.05 to 0.17 mm at most between the conventional key and the key groove in the width direction (rotational direction). Therefore, every time the rotational driving shaft is reversely rotated, the key is displaced by the distance corresponding to the gap within the key groove in the rotational direction, and undergoes a shock. The frequency of such reversing action may disadvantageously lead to a further enlarged gap. Accordingly, such conventional key is not applicable, in particular, to the precision instruments.